1. Field of the Invention
The present invention relates generally to a bar code detecting apparatus for and a bar code detecting method of detecting a variation in intensity of reflected light from a bar code, thereby reading the bar code and demodulating it into data. The present invention relates more particularly to a bar code detecting apparatus and a bar code detecting method that are capable of efficiently demodulating the bar code by logically eliminating data for intensity variation of reflected light which is generated due to elements other than the bar code.
2. Description of the Prior Art
In recent years, as represented by a POS system in the field of distributing business, etc., it is a common practice that commodities are managed based on bar codes. For example, in the POS system for commodities, data such as kinds, selling prices, etc. of the commodities are coded in a bar code format, and the encoded bar code is printed on the commodity or printed on a seal labeled to the commodity. Then, the bar codes are read at a checkout counter, and money is paid based on the read data. Then, the numbers of commodities sold are summed in real time, which serves for managing the stock and purchasing as well.
A bar code reader for reading such bar codes is roughly classified into a fixed type, employed for small comodities, and a handy or portable type employed for large commodities. The fixed type of bar code reader involves the use of a mechanism for scanning the bar code with irradiated reading light beams In multi-directions so that the bar code can be read even when the commodity is set over the bar code reader without an operator being aware of a direction of the bar code. More specifically, the fixed type uses a polygon mirror and fixed reflecting mirrors in combination. Then, the laser beams as the reading light beams are reflected by a single reflecting surface of the polygon mirror, during which the reflected light beams therefrom successively strike on a plurality of fixed reflecting mirrors in order and turned for scanning in a variety of directions by the respective fixed reflecting mirrors. This fixed type of bar code reader receives the reflected light beams from the surface of the commodity while performing the scan described above and inputs an item of intensity variation data of the reflected light beam received (hereinafter termed "reflected light data") to a demodulating circuit. This demodulating circuit demodulates the reflected light data on the basis of a bar code demodulation algorithm and extracts the data coded in the bar code format.
Such a fixed type of bar code reader is demanded for a higher performance when quickly reading the bar codes. For this purpose, there has hitherto been made an attempt to increase a probability (a bar code scanning probability) (at which the laser beams hit at the bar code of the commodity passing above the bar code reader) by increasing a laser scan velocity with high-speed rotations of the polygon mirror.
However, when such a high-speed scan is carried out, though the bar code scanning probability per unit time is enhanced, a whole quantity of the reflected light data per unit time increases because of the bar code scanning probability being fixed during a period of one revolution of the polygon mirror. The demodulating circuit has to demodulate all pieces of reflected light data augmented as described above, and, therefore, the high-speed scanning leads to a futile increase in processing load for the demodulating circuit and a rise in costs due to an arisen necessity for a scale-up (i.e., upgrading) of the hardware.
Further, in response to the demand for higher-performance for the bar code reader, there has been conducted such a complex demodulating process as to reproduce the data corresponding to the whole single bar code by connecting fragmented pieces of reflected light data based on the bar code (hereinafter referred to as "bar code reflected light data"). The above complex demodulating process, however, causes an increase in the processing load of the demodulating circuit. Accordingly, if such a demodulating process is executed for the reflected light data relative to the elements exclusive of the bar code, this leads to a futile rise in the processing load for the demodulating circuit.